Electrical servo system



Feb, 94?. E. J. UHMG ELECTRICAL SERV@ SYSTEM Filed April 30, 1945 INI 'EN IOR,

J Mw@ Eric z BY cig/ vPatented Feb. 22, 1949 ELECTRICAL SERVO SYSTEM Erich J. Uhlig, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of v Delaware Application April 30, 1945, Serial No. 591,064

This invention relates tov servo systems, particularly to servo systems for controlling a load in accordance with positional or other information.

One of the objects of the invention is the provision of an improved simple and reliable servo system of the character outlined. I

Another object of the invention is the provision, in a servo system of the character outlined, of mechanism for relieving pressure which might otherwise be applied to elements of the system due to the torque of rotating parts.

A further object of the invention is the provision of a servo system of the character outlined in which a minimum load is imposed on the synchro motor or other element employed to transmit or receive positional or similar intelligence.

The invention will be described in its application to apparatus which may be employed on an aircraft carrier, for example, and which includes a rotatable directional antenna system for transmitting bearing signals, and an antenna control unit for synchronizing the various signals transmitted with the direction of transmission of the signals with respect to a longitudinal reference line. The device of the invention provides a mechanical drive for the antenna control unit to compensate for any change in the course of the carrier. It is accordingly an additional object of the invention to provide improved radio beacon equipment of the character indicated, although the invention is not limited, or intended to be limited, to lthat particular application.

The objects of the invention are achieved by the provision of a synchro motor or similar de-f vice operated in accordance with positional or other intelligence transmitted thereto, and of a reversible servomotor for driving the load. The servomotor is driven by an amount and in a direction determined by rotation of the rotor of the synchro motor. The connection from the synchro to the servomotor includes mechanism, which will be described in detail hereinafter, for imposing a minimum load on the synchro motor and for preventing the application of undue pressure to elements of the system. In addition to driving the load, the servomotor is also provided with means for rotating the entire synchro motor, including the stator. in such a way as fo bring the system to rest when the desired compensation has been achieved.

The invention may be better understood from the following description of an illustrative embodiment thereof when read in conjunction with 2 Claims. v (Cl. 318-30) the accompanying drawing,4 the single ilgure of which is a view in perspective, though partly schematic, of a device according to the invention as applied to radio beacon equipment of the character previously mentioned.

In the device shown in the drawing, a gyrocompass transmitter or repeater I0 is connected to a synchro system including a synchro generator I2 and a synchro motor I'4. The motor has a rotor winding I6 and a rotor shaft I8, the winding being connected to a source 20 of alternating current.

A cam 50, which may be of stainless steel or other suitable sturdy material, is rigidly secured to the rotor shaft I8. The cam is shown as of cardioid shape, and is provided-with a depression 52 which supports a cam follower 48. In a practical case, the cam follower may be constituted by a ball bearing, and is secured to an elongated follower arm 44 which is connected at one of its ends by a pivot 42 to an end of a pivot arm 40. The opposite ends of the two arms, are resiliently connected, as, for example, by a spring 46. The pivot arm 40 is secured to a supporting plate 38 which forms a support for a movable contact 28 and is rigidly secured thereto.

The construction described is such as to permit the supporting plate 38 and therefore the movable contact 28 to move freely about a horizontal axis coincident with the shaft I8 as indicated by arrows 16. This movement will be in response to rotation of the rotor members I 8 and I8 transmitted to the plate through the cam follower 48, follower arm 44 and pivot arm 40. The supporting plate is provided with a projection 'l2 to which springs 68 and 'l0 are secured. These springs exert balanced forces on the supporting plate, and serve to keep the movable contact centered in the absence of any force derived from rotation of members I8 and IB. The projection 'I2 may be of magnetic material, and is preferably equally spaced from a pair of opposing. pole pieces constituted by a permanent magnet 14.

A servomotor 22, which may be any type of `reversible motor, is connected to derive power from any appropriate source, such as the alterhating current source 20. One lead 24 from the source 2D goes directly to the field Winding of the servomotor, while .another lead 26 connects the source of alternating current by means of a flexible lead 82 with the movable contact 28, which is equally spaced between a pair of stationary contacts 30 and 32. Leads 38 and 34 are taken from the contacts 30 and 32 respec- 3 tively to the servomotor. When the movable contact 28 is in conductive engagement with the stationary contact 30, the servomotor is driven in one direction, but when it is in engagement with the other contact 32, the servomotor is driven in the opposite direction. n the other hand when the movable contactv is out of engagement with either stationary contact, the power input circuit is open and the motor is at rest.

An output shaft 80 of the motor 22 is provided to drive a load constituted by a unit 84 which is adapted to control the operation ofan antenna assembly 66. The shaft 80. is mechanically coupled to the frame of synchro motor Il, as for example by a worm gear 62 which is mounted on the shaftl 60 and is driving relation with a helical gear 58 rigidly secured to the frame of the synchro motor. Driving of the servomotor causes rotation of the entire synchro motor, including the stator winding, about its longitudinal axis. The coupling is such that when the synchro generator is adjusted so as to cause the rotor members I6 and I8 and therefore the cam 50 to be rotated in one direction, with respect to the stator, the gear 58 and the whole of the motor I4 including the stator are driven in the opposite direction by the servomotor. By way of example, anarrow 'I8 shows the cam 50 rotated in an anticlockwise direction at the same time as the helical gear 58 is driven in a clockwise direction, as indicated by an arrow 80.

The operation of the device described is as follows: A particular ships course or a longitudinal line is taken as a standard of reference.l Ordinarily this will be when the vessel on which transmitted from the gyro-compass through the synchro generator. The cam 5I) begins to rotate a corresponding amount and in a corresponding direction, a rotational torque is exerted onl the cam follower '48 and the movable contact 28 is brought into engagement with one or other of the stationary contacts and 32. The servomotor 22 is thus energized to drive the load 64, the direction in which it is driven depending upon whether the movable contact is brought into engagement with one stationary contact 30, or with the other stationary contact 32.

4 follower will rideout of the depression 52 and permit the rotor to turn without exerting excessive force on the contacts.

The elements connecting the rotor shaft I8 to the movable contact 28 may be thought of as in two groups: the cam and cam follower and the follower arm 44 are in one group, and the pivot arm 40 and the supporting plate 38 are in the other group. The spring 46 forms the connecting link between the two groups, and the tension of the spring may be adjusted according to whatever pressure it is desired that the movable contact shall exert on either of the stationary contacts.

As long as the cam follower is supported within the depression 52, and the cam is not exerting a rotational torque on the cam follower, the springs 68 and 'I0 exert balanced forces upon the contact plate, keeping the movable contact out of engagement with either of the stationary con tacts. By this means undesired energization of the servomotor is avoided. As soonhowever as the cam is rotated, even slightly, the magnetic projection I2 is brought nearer to one of the pole pieces of the permanent magnet 1d than to the other. The magnetic forces thus brought into action accelerate the movement of the supporting plate, and the magnet therefore acts as a toggle to bring the movable contact into firm engagement with one or other of the stationary contacts.

As soon as either of the two power input circuits of the servomotorA is closed, that motor begins to drive the load, and continues to do so until the cam and camfollower are returned to their original positions, by reason of rotation of the whole of the synchro-motor Il through the gearing 58-60. The movable contact then comes out of engagement with either of the stationary contacts, the servomotor is deenergized, andthe springs 68 and 10 regain control and hold the movable contact centered away from either stationary contact.

To prevent coasting of the servomotor after it has been deenergized, or hunting about the point of rest, it is desirable that the servomotor shall have an armature with low inertia, for example one made of the alloy known as Alnico." Alternatively a brake or other device may be coupled to the output shaft 80 lto provide a frictional force 'in opposition to lthe torque of the servomotor. v

The invention may thus be described as a mechanical servo system employing a synchro motor provided with elements rotatable under the influence of intelligence transmitted to the syn- 'chro motor, and a reversible servomotor for If the movable contact 2B were connected directly to the rotor shaft I8 of the synchro motor, the pressure oi the movable contact on either of the stationary contacts` would be a function of the torque exerted by the synchro motor. If the ships course -were changed suddenly and by a substantial amount, that pressure might ybe sufficient to cause faulty operation, and

in an extreme case might cause breakage of parts v driving a load.v The servomotor has a power input circuit including a movable contact yieldably coupled to the rotor members of the synchro motor by a self-centering pressure-relief mechanism comprising the cam and associated elements hereinbeforc described. In addition to driving the load, the vservomotor also drives the whole of the synchro motor through gearing to bring it back to a `centered position, at which point the servomotor is brought to rest.

I claim as my invention:

1. The combination of a synchro motor provided with a stator and a rotor, a cam rigidly coupled to said rotor and having an outline including a depression, a cam follower normally resiiiently supported within said depression, a reversible motor having a drive shaft for driving a load and a power input circuit including a pair 5 of stationary contacts and a movable contact, a supporting plate forming a support for said movable contact and two arms pivotally connected to each other at one end, one of said arms being secured to said plate and the other of said arms being secured to said cam follower, and `means for applying to said plate balanced spring pressure in opposite directions to maintain said plate in a normally centered position, whereby rotation of said cam in one-direction brings said movable contact into engagement with one of said stationary contacts to energize saidreversible motor and drive said shaft in one direction, and movement of said cam in the opposite direction brings said movable contact into engagement with the other ,said stationary contacts to energize said reversible motor and drive said shaft in the opposite direction, and means responsive to the rotation of said shaft for rotating said stator in a direction opposite to that of said cam whereby to return said cam and cam follower to their original relative positions to bring said movable contact out ofy conductive engagement with either of said stationary contacts.

2. The invention as set forth in ciaim 1 where-A in at least a portion o! said supporting plate is of magnetic material and a permanent magnet is provided with pole pieces on opposite sides of said 5 portion.

10 iile oi this patent: f

UNITED STATES PATENTS Number Name Date 1,559,525 Murphy et al Oct. 27, 1925 5 1,725,256 Claytor Aug. 20, 1929 1,954,142, Moiett Apr. 10, 1934 2,194,170 Newell Mar. 19, 1940 2,412,605 Drake Dec. 17, 1946 o FOREIGN PATENTS Number Country Date France Apr. 23, 1921 

